In the tool industry, it is common to provide a fluid bearing for use to assist in supporting tool components during boring, drilling, reaming or other machining operations. Advantages for utilizing such bearings are created since a pressurized fluid film normally separates the components and prevents physical contact, that, in turn, reduce physical wear and tear on the tool components used in the machining operations. Establishing a fluid bearing also permits operating components at increased rotational speeds without negatively affecting accuracy, reduces the influences of contamination (e.g., particles or chips abrading the surfaces), allows for increased loads to be placed on a tool, and further controls thermal energy.
A fluid bearing is a system in which moving components, such as a rotor in a tool assembly, are physically separated from the non-moving components (e.g., a stator) by a load carrying film of pressurized fluid. By controlling fluid pressure, the components (e.g., the rotor) in the bearing can be supported to assist in maintaining tool rigidity and to minimize wear on the components. To achieve the film "floating effect" in a fluid bearing, a certain amount of pressurized fluid must generally be permitted to drain or leak from the fluid bearing, and thus, it is necessary to replace these fluids lost in order to maintain the supporting pressures within the fluid bearing.
In the past, pressurized fluids have been delivered to the bearing chamber between the stator and rotor through passages in the stator. Examples of these arrangements are shown in U.S. Pat. No. 3,438,287 to Kampmeier, et al., U.S. Pat. No. 3,488,288 to Kaiser, and U.S. Pat. No. 3,438,289 to Kampmeier, wherein fluid flows through the stator and is directed inwardly toward the rotor to provide a fluid bearing in the pressure pads and space between a spindle and its bushings in two hydrostatic bearing supports positioned at opposite ends of a workpiece. Seemingly, the supports at opposite ends of the workpiece are required to create a hydrostatic bearing to effectively support the rotor.
If the workpiece must be transported from machine to machine (as is often the case where multiple machining operations are required), a stator supplying fluid for the fluid system would have to accompany the workpiece as it is moved. These structural requirements could possibly require an extensive and complex network of supply hoses so that fluid communication could be established and maintained once the workpiece was set up on the next machine, or alternatively, each would require severing fluid communication to the stator, moving the stator, and the reestablishing fluid communication to the stator. These steps are burdensome, labor intensive, time consuming and increase the overall cost of machining, or of the machine itself.
As can be seen, currently available machining tools that require fluid bearings have a number of shortcomings which greatly reduce the flexibility and versatility of these tools. Moreover, current machining operations demand tool systems which can operate at increased rotational speeds or revolutions per minute "rpm" to achieve desired levels of performance and results. The cumbersome structural and hydraulic arrangements heretofore available are not easily adapted for high production applications, and are increasingly incompatible in modern manufacturing processes. The industry currently lacks a machining tool which is usable in a quick change tool center that can operate at increased speeds, and that can form a transient fluid bearing in the bore hole of a workpiece for a machining tool, especially a boring tool with an extended length.